Non-patent publications and other reference materials referred to herein, including reference cited therein, are incorporated herein by reference in their entirety and are referenced in the following text and respectively grouped in the appended Bibliography which immediately precedes the claims.
Unmanned Ground Vehicles (UGVs) are being used in various applications, including space explorations, military missions, agriculture, and subterranean missions. Off road vehicles have been investigated for a long time, both for wheeled and tracked vehicles. While wheels are efficient for motion on relatively smooth and flat surfaces, tracked vehicles offer several advantages for motion on rough terrains. However, autonomous unmanned tracked vehicles introduce some drawbacks that limit their use. In particular, positioning and motion control for tracked vehicles are complex due to the nature of the slip during skid-steering. Some models for slip estimation have been developed (Yoshida, 2001, Shiller and Serate, 1995), but they require sufficient data on the surface traversed by the vehicle.
Some systems improve performance and autonomy of the UGV by acquiring information from the terrain through identifying soil parameters using physical models and numerical techniques. Among other researchers, Tan et. al. (2003) use on-line identification systems to estimate friction coefficients in excavation missions.
It has been recognized that one way to overcome some of the difficulties encountered in traversing rough terrain using tracked robotic vehicles is to operate two or more of the vehicles in tandem. Advantages of operating in this manner include providing a wider effective wheel base to prevent the vehicle from overturning and that the vehicles can help each other overcome obstacles such as steep up or down slopes by employing a push-pull effect. Such an arrangement is described in U.S. Pat. No. 6,523,629. Coupling between the two robots is by means of two mating elements one mounted at the center of the back of the platform of the leading robot and the second at the center of the front of the trailing robot. Two configurations for the coupling device are described. A ball and socket configuration, which allows a maximum angular motion between the two robot platforms, and a ball and socket configuration, which permits vertical motion but not horizontal motion. The coupling device can either be passive or active. In the active mode, the coupling device is actuated by gears driven by a gear motor. The coupling between the two robots has several drawbacks including:                In either the passive or active mode there is no relative lateral motion between the two tanks and the angular motion of one robot is constrained by the other robot, resulting in restricted maneuverability while engaged.        No mechanism exists for relative configuration measurements between the two robots; therefore, that the accuracy of the whole system is limited.        
It is a purpose of this invention to provide unmanned tracked vehicles which overcome some of the drawbacks of the prior art.
It is another purpose of the invention to provide a mechanical linkage between two tracked driving units that allows improved mobility, accuracy and efficiency of autonomous robotic missions.
It is a further purpose of the invention to provide unmanned tracked vehicles capable of effectively performing autonomous robotic missions in unknown environments, particularly in confined spaces such as tunnels and pipes.
Further purposes and advantages of this invention will appear as the description proceeds.